1. Technical Field
The present invention relates to an apparatus for inflating an inflatable vehicle occupant restraint, such as an air bag. In particular, the present invention relates to a dual stage inflator for inflating an air bag.
2. Description of the Prior Art
Augmented inflators (also known as hybrid inflators) for inflatable occupant restraint systems are known. One such known inflator is disclosed in U.S. Pat. No. 3,901,530 and includes a first chamber containing inflation fluid stored under pressure. The inflator also includes a central housing that has a mixing chamber and flow passages communicating the first chamber with the mixing chamber. The central housing includes a diffuser which directs inflation fluid from the mixing chamber to an inflatable vehicle occupant restraint, such as an air bag. A first gas barrier blocks the flow of the inflation fluid from the mixing chamber to the diffuser.
The central housing has a pyrotechnic material in a second chamber to produce a combustion gas upon ignition. The second chamber and pyrotechnic material are isolated from fluid communication with the mixing chamber by a second gas barrier. Upon ignition of the pyrotechnic material by a squib, the gas barriers rupture to provide heat to the inflation fluid as the inflation fluid flows into the air bag. In this inflator, both of the gas barriers rupture at approximately the same time. Therefore, the timing of the pressure increase of the inflation fluid in the air bag is fixed and cannot be varied to accommodate conditions within the vehicle that may change.